Metaxytherium
Metaxytherium | |
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M. floridanum fossil | |
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Genus: | Metaxytherium De Christol 1840
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Metaxytherium is an
Discovery and naming
The first remains of Metaxytherium were described in 1822 by Anselme-Gaëtan Demarest as a species of Hippo, H. medius before the genus name Metaxytherium was coined in 1840 by De Christol. Although the type species was initially designated to be M. cuvieri, later publications argued that the two species are synonymous and M. medium thus holds precedence. The grammatical changes of the species name were made to match the rules of the International Code of Zoological Nomenclature (ICZN).[2]
M. serresii was introduced by Gervais in 1847 to encompass the Metaxytherium finds made in Montpellier, France from the Early Pliocene. Although he later described and figured multiple specimens, no type specimen was ever introduced. M. floridanum was named in 1922 by Oliver P. Hay based on a piece of a right maxilla discovered 11 years prior near Mulberry, Florida.[3] The genus Thalattosiren, described by Sickenberg in 1928, was erected from remains previously named M. pettersi, however, further research concluded that it should not only be synonymous with Metaxytherium on a genus level, but is also indistinguishable from M. medium as a species.[4] M. arctodites was named in 1994 by Aranda-Manteca, Domning and Barnes based on three specimens found in
The name Metaxytherium means "inbetween beast" or "intermediate beast" from the Greek μεταξύ (metaxy) and θηρίον (therion). The name derives from the original interpretation of it being an intermediate form between dugongs and manatees.[6]
There are several genera that are now synonymous with Metaxytherium, including Thalattosiren,[4] Halianassa, Felsinoitherium, Cheirotherium and Hesperosiren.[5] Several species previously considered distinct have likewise been synonymized with already established Metaxytherium species.
Species
- M. albifontanum
- Described in 2014, this species inhabited what is now Florida and South Carolina during the late Oligocene. The species name "albifontanum" is a composite of the Latin "albus" (=white) and "fontanus" (=of a spring), a name chosen due to the holotype being discovered near White Springs, Florida. More specifically, M. albifontanum was discovered in the Porters Landing Member of the Parachucla Formation and the Chandler Bridge Formation of South Carolina (25.7-23.6 Ma). It is the stratigraphically oldest species of Metaxytherium and relatively small, with a body size of 2 to 3 meters.[1]
- M. arctodites
- M. arctodites is found in mid Miocene (15 - 14 Ma) layers of California and Baja California, specifically the toothed whales and pelagic sharks.[5]
- M. crataegense
- A West-Atlantic species found in the early to middle Miocene Montera Formation of Peru[7] as well as the Hawthorne and Calvert formations of the United States, extending its range from western South America to the north-east of the United States.[8] M. crataegense existed from the approximately late Hemingfordian (ca. 20.44 Ma) to the early Barstovian (ca. 13.6 Ma).[9] The two species M. calvertense and M. riveroi from Cuba have both been sunk into this species as well.[10]
- M. floridanum
- Named after the state of Florida, M. floridanum is found in the middle to late Miocene rock layers of northern and central Florida with many remains being found in the phosphate mines of Central Florida,[11][12] belonging to the Lower Bone Valley Formation.[13] M. floridanum remains specifically date to the Late Barstovian to Early Hemphillian age (14-7 Ma).[14] It reached a length of approximately 3 meters.[15]
- M. krahuletzi
- M. krahuletzi is the oldest species of Metaxytherium known from Europe,[4] inhabiting the shallow waters of the Central Paratethys as well as nearby waters. The vast majority of M. krahuletzi fossils have been collected from the Burgschleinitz Formation of Eggenburg Bay, Austria. Fossils date to the Eggenburgian Age (20.8 - 18.3 Ma) to the Ottnangian (18.3 - 17 Ma). A specimen from France tentatively referred to M. cf. krahuletzi dates to the Karpatian Age, roughly 17.5-16.5 Ma.[16] The Metaxytherium bonebeds of Eggenburg Bay have been suggested to represent mass death sites, possibly the result of reduced food supply following heavy storm events known to have occurred in this part of the Paratethys.[17] The species was named in honor of Austrian geologist Johann Krahuletz.
- M. medium
- The type species, M. medium is known from the Middle Miocene (Langhian)[4] of Western and Central Europe (France, Netherlands, Austria),[18] Greece[19] and presumably Northern Africa. The most recent records of M. medium stem from late Miocene (Tortonian) Tuscany (10.5 to 8.14 Ma).[20]
- M. serresii
- A species originally described to include Pliocene (Early Zanclean) specimen from Marcel de Serres.[22]
- M. subapenninum
- M. subapenninum, the last species of Metaxytherium in the fossil record, lived in the early and late Pliocene of Italy and Spain. It is the only species of sirenians that lived in the northwestern coasts of the Mediterranean Sea in the Pliocene and disappeared from the Mediterranean around 3 million years ago because of the progressive climate cooling. Fossils of these dugongs have been found in various parts of Italy, Spain and possibly on the island of Mallorca. M. subapenninum marks a return to greater body size in European Metaxytherium (4-5 meters) and possesses the largest tusk of this particular lineage.[23]
There are tentatively referred specimens from the early Miocene Pirabas Formation of Brazil and undetermined remains from the middle Miocene Parana Formation of Argentina.[8]
Evolution
The exact origins of Metaxytherium are complicated and not entirely understood, with the two basal-most species being known from opposite sides of the
Research conducted prior to the description of M. albifontanum instead generally suggested a European origin of Metaxytherium, possibly derived from Lentiarenium christolii (previously Halitherium) and eventually forming an anagenetic lineage of European and North African sirenians.[4] While M. krahuletzi and M. medium go through only relatively slight morphological changes, M. serresii represents a strange diversion from the overall trend observed among the European Metaxytherium
The presence of Metaxytherium species on the western coast of the Americas, in addition to their close phylogenetic ties with the Hydrodamalinae, has been suggested to represent a second anagenetic lineage starting with M. crataegense entering Peru via the Central American Seaway. M. arctodites has been hypothesized to be a direct descendant of this species found further north along the Mexican and Californian coastline. The hypothesis also suggests that this northern lineage would further give rise to Dusisiren and eventually culminate in the algae specialist Hydrodamalis, which persisted until historic times. Unlike the European forms, which continuously evolved larger tusks to deal with the environmental changes of the Late Miocene Mediterranean, the American lineage took a different approach, gradually shrinking their tusks until losing their teeth entirely in Hydrodamalinae.[10][5]
Phylogeny
Phylogenetic analysis suggests that Metaxytherium is a
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The following phylogenetic tree is a simplified version of the results produced by Kerber and Moraes–Santos (2021), recovering similar results with the exception of a polytomy within Metaxytherium, similar to that recovered by Sorbi et al. (2021).[26] In their phylogeny Sirenia is limited to manatees and dugongs.
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Paleobiology
Diet
Unlike modern sirenians, Metaxytherium is known from a multitude of environments that it shared with other species of sea cows. M. albifontanum for instance coexisted with both
In a 2004 publication MacFadden and colleagues attempted to determine diet and habitat of the extinct sirenians of Florida using isotopic values. Concerning Metaxytherium, both M. crataegense and M. floridanum were analyzed. In modern taxa, dugongs show a sharply downturned upper jaw, generally associated with its grazing lifestyle, while
The diet of the European lineage meanwhile followed a clearly observable trend from the Miocene to the Pliocene. Early taxa such as M. krahuletzi and M. medium had small tusks and likely fed on the leaves of seagrasses as well as small to medium-sized rhizomes. The Tortonian and Messinian Salinity Crisis may have caused shifts in the seagrass flora of the Mediterranean Basin, leading to a greater percentage of rhizomes in the diet of Metaxytherium and causing the "medium" sized tusk-condition seen in M. serresii. As conditions in the Mediterranean stabilized, previously dominant seagrasses such as Posidonia oceanica recolonized the area and become a key component in the sirenian's diet. M. subapenninum could have developed its larger tusks to specifically feed on the thick and nutrient rich rhizomes of Posidonia rather than returning to their previous diet. This would have been furthermore beneficial as Posidonia provided a relatively stable food source compared to some of the other seagrass species, which fluctuate in availability between seasons.[23]
Predation
In 2012 the disarticulated skeleton of a young Metaxytherium, tentatively referred to M. cf. medium due to its stratigraphic position in the
See also
References
- ^ S2CID 86498351.
- )
- ISSN 0096-3801.
- ^ a b c d e Domning, D. P.; Pervesler, P. (2012). "The sirenian Metaxytherium (Mammalia: Dugongidae) in the Badenian (Middle Miocene) of Central Europe" (PDF). Austrian Journal of Earth Sciences. 105 (3): 125–160.
- ^ a b c d Aranda-Manteca, F.J.; Domning, D.P.; Barnes, L.G. (1994). "A new middle Miocene sirenian of the genus Metaxytherium from Baja California and California: relationships and paleobiogeographic implications". Proceedings of the San Diego Society of Natural History. 29: 191–204.
- .
- ^ De Muizon, C.; Domning, D.P. (1985). "The first records of fossil sirenians in the southeastern Pacific Ocean". Bulletin du Muséum national d'Histoire naturelle. 7: 189–213.
- ^ .
- S2CID 134274604.
- ^ .
- ^ S2CID 17889395.
- ^ "Palmetto Fauna". Florida Museum. 2017-03-27. Retrieved 2021-06-15.
- JSTOR 1373704.
- ^ Rojas, Alexis; Hulbert Jr., Richard C.; Valdes, Natali (March 2, 2015). "Metaxytherium floridanum". Florida Museum. Florida Museum of Natural History Gainesville, FL 32611: University of Florida. Retrieved 19 April 2021.
{{cite web}}
: CS1 maint: location (link) - JSTOR 4523227.
- ^ Sorbi, S. (2008). "New record of Metaxytherium (Mammalia, Sirenia) from the lower Miocene of Manosque (Provence, France)" (PDF). Geodiversitas. 30 (2): 433–444.
- ^ Pervesler, P.; Roetzel, R.; Domning, D.P. (1999). "Palaeontological Highlights of Austria: Lower Miocene Seacows from Austria" (PDF). Austrian Journal of Earth Sciences. 92: 213–215.
- ^ Hoojer, D.A. (1977). "A sirenian skeleton from the Miocene of Eibergen, Province of Gelderland, The Netherlands: Metaxytherium cf. medium (Desmarest)". Scripta Geologica. 41: 1–25.
- ISBN 978-3-030-68398-6.
- .
- ^ .
- ^ Gervais, Paul (1847). "Observations sur les mammifères fossiles du midi de la France". Extrait des Annales des Sciences Naturelles. 8.
- ^ S2CID 84318304.
- ^ Bianucci, G.; Carone, G.; Domning, D.P.; Landini, W.; Rook, L.; Sorbi, S. (2008). "Peri-Messinian Dwarfing in Mediterranean Metaxytherium (Mammalia: Sirenia): Evidence of Habitat Degradation Related to the Messinian Salinity Crisis". Garyounis Scientific Bulletin (5): 145–157.
- ISSN 0077-7749.
- S2CID 236226810.
- ^ PMID 22319622.
- S2CID 233664574.
- S2CID 239648451.
Further reading
- Manatees and Dugongs of the World by Jeff Ripple
- Discovering Fossils: How to Find and Identify Remains of the Prehistoric Past (Fossils & Dinosaurs) by Frank A. Garcia, Donald S. Miller, and Jasper Burns
- Encyclopedia of Marine Mammals by William F. Perrin, Bernd Wursig, and J. G.M. Thewissen
- Marine Mammals: Evolutionary Biology by Annalisa Berta, James L. Sumich, and Kit M. Kovacs
- Marine Mammal Biology: An Evolutionary Approach by A. Rus Hoelzel
- Neptune's Ark: From Ichthyosaurs to Orcas by David Rains Wallace
- Classification of Mammals by Malcolm C. McKenna and Susan K. Bell